A large scale habitat manipulation was conducted to assess
the effects of establishing an emergent macrophyte, American water willow
Justicia americana, on littoral reservoir assemblages. Coves
in three large (>1,800 ha) Kansas impoundments were chosen and half planted
with water willow. Sampling was conducted during the summer from
2001 to 2004. I found that water willow coves had more complex
habitat as well as higher abundance and diversity of fishes, macroinvertebrates,
and zooplankton than control coves. However, strong temporal variation
in water levels influenced the amount of inundated water willow available
in these systems. The effects of water willow on density, growth,
condition, and diet of age-0 largemouth bass Micropterus salmoides
were assessed. Significantly higher densities of age-0 largemouth
bass were found in water willow coves, but growth, condition, and diet
did not differ between water willow and control coves. Therefore,
water willow was able to support higher abundances of age-0 largemouth
bass than control coves without affecting growth, condition, or diet.
Characteristics of age-0 largemouth bass from the water willow coves were
compared to those from two small impoundments (<80 ha) with abundant
macrophyte and healthy largemouth bass populations. Small impoundments
had higher densities of age-0 largemouth bass than water willow coves in
the three large impoundments, but individuals on average also had lower
growth, condition, and fewer fish in their diet. Thus, largemouth
bass populations in small impoundments may be more regulated by density
dependent factors than populations in large impoundments. Overall,
water willow is beneficial to littoral areas, supporting an increase in
both abundance and diversity of assemblages. Finally, I used a field
experiment to test the inundation and desiccation tolerance of water willow
for different depths and durations. Water willow was susceptible
to inundation, but resistant to desiccation. My findings provide
information that can be used to select candidate reservoirs for water willow
establishment based on expected water-level fluctuations.